Plumbing valves

Plumbing systems will have a series of valves controlling the water flow throughout the property. This includes isolating sections of the pipe run for maintenance. The most important valve is the stop valve that controls the flow of water from the mains supply into the property. In the event of an emergency it is important that you know where to find the stop valve.

Stop valve

All properties will have a stop valve for controlling the flow of water from the mains supply into the building. Large properties often have more than one stop valve controlling the water flow to particular areas of the system. Most stop valves will have a traditional tap handle. Usually the stop valve is fitted with a compression joint. When installing the stop valve, it must be fitted the way round in relation to the direction of the water flow. There will be an arrow on the valve indicating the correct direction.

Isolating valve (also called a service valve)

Isolating valves come in a range of designs and are used for shutting off the water supply to small areas of the plumbing system. For example if a tap needs replacing, then its water supply would firstly need to be turned off, so the valve located close to the tap would be used to achieve this. Isolating valves can be metal or plastic but it is important to remember that some plastic valves are only suitable for hot water up to a certain temperature, which will be indicated on the outside of the valve. In older plumbing systems isolating valves may have tap handles but more modern valves are opened and closed using a slot-head screwdriver. When the slot is in line with the pipe the valve is open and closed when it is at 90° to the pipe. As with the stop valve, isolating valves must be fitted correctly in relation to the flow of water and this is indicated by an arrow on the outside of the valve.

Gate valve

This type of valve does a similar a job as a stop valve but they are designed for low-pressure pipes e.g. supply pipes from a storage cistern. Unlike other valves, gate valves can be fitted either way round. Gate valves can be easily identified by their red wheel handles.

Drain valve

Drain valves are positioned on a pipe run so the system can be drained when required. They are located where the plumbing system cannot be drained from kitchen or bathroom taps and are most commonly found connected to the boiler or central heating system. Attaching a hose to the nozzle of the drain valve and turning the valve using a valve key will successfully drain that part of the system.

Non-return valve (also called a check valve)

The function of a non-return valve is to prevent back siphonage into a supply pipe causing the water supply to become contaminated. A non-return valve only allows the water to flow in one direction. Used mainly with outdoor taps and mixer taps the non-return valve is usually built into the design of these types of fittings.

Toilet cisterns

Cold water cisterns such as the toilet cistern and a loft storage tank will be fitted with two valves: an inlet or float valve controlling the correct amount of water flowing into the cistern when it is filling up, and an outlet valve that opens up when the water is leaving the cistern. There are a variety of inlet and outlet valves available but generally the different mechanisms work on the same principles. The most common inlet and outlet valves found in toilet cisterns are described below.

Brass lever arm and ball float valve

A ball float is attached to a brass arm. When water leaves the cistern the ball float drops with the water level, opening a piston in the valve allowing water to flow into the cistern. As the cistern fills up with water the ball float rises gradually closing the valve.

Siphon valve

A siphon valve has a handle positioned on the outside of the cistern, which is attached to a lever on the inside. The lever has a wire linked to a rubber flap valve. When the handle is depressed the lever lifts the rubber flap valve allowing water to flow from the cistern into the siphon, where atmospheric pressure draws it up through the siphon, down the outflow pipe and into the toilet bowl.